In the laser modules currently known in the art, the laser chips are mounted on at least one of the electrodes by soldering, which causes various problems.
The main problem caused is that the laser chip must be placed with very high precision, in such a way that its end projects from the end of the electrode, so that the soldered connection which will join it to said electrode does not reach laser chip emission zone, for if it does so the laser module will be defective.
At present, in order to position the laser chip correctly in relation to the electrodes and their soldered connection with acceptable precision it is necessary to have available micro-robots and other high-precision appliances, which calls for a very considerable investment and thus has a marked effect on the end price of the product.
The soldered connection of the laser chip does not permit subsequent adjustment of its position or replacement of the chip in the event of failure. At present, if the chips have been positioned incorrectly or if they have failed the entire laser module has to be replaced, with the consequent losses.
Another problem currently encountered arises due to the different expansion coefficients of the laser chip material and of the electrode material. This difference results in the possibility of alterations in the laser chip, usually in its refractive index.
Some normal problems related to the difference in the expansion coefficients are the residual mechanical stress resulting from the soldering process, and also the mechanical stress induced when the laser is pulsed during operation, being both problems due to thermal expansion mismatch between the soldered materials. The residual mechanical stress causes a lifetime reduction of the laser chip. The residual mechanical stress also causes some curvature in the laser chip, called “smile” and this affects negatively to the beam shaping of the laser module.
In order to reduce the difference in the expansion coefficients and their aforesaid problems, special materials for the electrodes are used, for example copper alloys with tungsten, but such alloys present bad thermal conductivity and therefore the corresponding laser modules have bad thermal parameters.
Other general problem of the soldering process is the high temperature reached during this process, which results in the creation of defects in the laser structure.